Paper webs or sheets, usually called tissue or paper tissue webs, are commonly used in paper towels, napkins, facial and toilet tissues. The important characteristics for such papers are softness, absorbency and strength. There is an ongoing work to improve each of these characteristics without seriously affecting the others.
Conventionally pressed tissue paper and methods for making such paper are well known in the art. Such paper is typically made by draining and forming a cellulosic suspension on a wire. The cellulosic suspension is usually contained in the headbox before being deposited on a Fourdrinier wire to form a paper web. The paper web is then typically dewatered by vacuum dewatering and further dried by pressing operations wherein the web is subjected to pressure developed by opposing mechanical members, for example cylindrical rolls or an extended nip press. The dewatered web is then further pressed and dried by a steam drum apparatus known in the art as a Yankee cylinder.
Conventional fluff and methods for making such paper are well known in the art. Such paper is typically made by making a paper sheet on a Fourdrinier wire and subsequently pressing and drying the paper sheet into bales or rolls. The dry paper is then defiberized using a hammermill or a pin defiberizer to form fluff. Typical products made from fluff are diapers and feminine hygiene products. Fluff can also be used to produce air laid paper products.
Softness is a tactile sensation perceived by the consumer holding a particular product, rubbing it across the skin or crumpling it within the hand. Softness of a sheet can be achieved by mechanical means. For example, the sheet can be calendered to flatten the crests formed when creping the sheet. The sheet can also be frictionally treated in order to eliminate any roughness. However, these approaches are often insufficient.
One way to make the paper softer is to add a softening compound to the cellulosic suspension. The softening compound interferes with the natural fibre-to-fibre bonding that occurs during sheet formation in papermaking processes. This reduction of bonding leads to a softer, or less harsh, sheet of paper.
WO 98/07927 describes the production of soft absorbent paper products using a softener. The softener comprises a quaternary ammonium surfactant, a non-ionic surfactant as well as strength additives. The softening agent is added to the cellulosic suspension before the paper web is formed.
A softening compound can also be applied to a dry or wet paper web e.g. by means of spraying. If the paper web is dry, the softening compound can also be printed on the paper.
U.S. Pat. No. 5,389,204 describes a process for making soft tissue paper with functional-polysiloxane softener. The softener comprises a functional-polysiloxane, an emulsifier surfactant and surfactants which are noncationic. The softener is transferred to the dry paper web through a heater transfer surface. The softener is then pressed on the dry paper web.
WO 97/30217 describes a composition used as a lotion to increase the softness of absorbent paper. The composition comprises an emollient which is preferably a fatty alcohol or a waxy ester. The composition also comprises a quaternary ammonium surfactant as well as one or more non-ionic or amphoteric emulsifiers.
Most softening compounds, either added to the cellulosic suspension or applied to the paper web, contain quaternary ammonium surfactants. Since producers and consumers experience a growing environmental concern, quaternary ammonium surfactants are not always accepted. The quaternary ammonium surfactants are generally toxic to aquatic organisms and are generally considered undesired chemicals.
It is an object of the invention to provide a composition for enhancing softness of a paper product.
It is a further object of the invention to provide a composition substantially free from quaternary ammonium surfactants.
Yet another object of the invention is to provide one single composition suitable for addition to the cellulosic suspension and applied to a wet or dry paper web, rather than several different compositions as described in the prior art.
Yet a further object of the invention is to provide a composition that has a high tolerance towards anionic carryover from preceding production stages. Standard formulations can thus be neutralised in the wet end when small amounts of detrimental substances are released from the preceding production stages.
It is also an object of the invention to provide a composition that, when added to the cellulosic suspension, will impart low burst strength, high wetting rate as well as low defiberization energy to the paper to be produced.
It is also a further object of the invention to provide a composition that, when added to the cellulosic suspension, will impart a low knot content to the product.